Elucidation of the mechanisms which regulate neural cellular proliferation during brain maturation is a prerequisite for understanding the pathogenesis of inherited and acquired disorders of cerebral development. Glial proliferation represents the major contribution to mammalian brain growth, and is recapitulated in dissociated cell cultures of developing rodent brain. This proposal will investigate regulation of glial cell cycling in primary and secondary neural cultures. Thus, at sequential immunocytochemically confirmed stages of glial maturation, progression through distinct phases of the cell division cycle will be examined by application of cell synchronization techniques. The kinetics of cell cycle progression will be determine by [3H]-thymidine autoradiography and by flow cytometry. By examining the timing during the cell cycle of the mitogenic actions of specific extracellular trophic factors and the synergisms between such agents, intracellular regulatory pathways involved in glial proliferation will be identified. While partly characterized in extraneural cells, the nature of proliferation-specific intracellular regulatory pathways in developing neural cells in unknown. To investigate control of these critical processes during development, these experiments will extend preliminary studies which demonstrated a requirement, at a circumscribed time in the cell in developing astrocytes, for nonsterol derivatives(s) of the isoprenoid biosynthetic pathway. To determine whether intracellular isoprenoid derivatives contribute to regulation of cell cycling during glial development, the relation of this requirement to actions of trophic factors at sequential stages of development in culture will be investigated. In addition, by determining flux of radiolabelled mevalonate into specific isoprenoid derivatives in glia stimulated to divide under conditions of inhibition of endogenous isoprenoid synthesis, this proposal will attempt to identify the isoprenoid derivatives involved in cell cycle phase-specific growth regulation at distinct stage of glial maturation. Thus, new information regarding the processes which regulate proliferation of developing glial cells will be obtained.